eMedicine Specialties > Radiology > Musculoskeletal
Pelvis, Insufficiency Fractures: Imaging
Updated: Mar 25, 2009
Radiography
Findings
Radiographic findings depend on the site of the fracture.
- Parasymphyseal and pubic ramus fractures may have an aggressive appearance, depending on the stage of fracture maturity.
- Findings include sclerosis, lytic fracture line, bone expansion, exuberant callus, and osteolysis (see Image 1).
Anteroposterior radiograph of the pelvis demonstrates areas of sclerosis in both sacral alae. Parasymphyseal fractures oriented vertically are seen as linear areas of osteolysis and adjacent sclerosis (arrows). Insufficiency fractures subsequently were confirmed on bone scans and CT.
- The most common finding is a sclerotic band or line.
- A lytic fracture line or cortical break rarely is observed.
Degree of Confidence
The degree of confidence is low. Sacral fractures are difficult to detect because of osteoporosis, overlying bowel gas, and calcified vessels.
False Positives/Negatives
Parasymphyseal and pubic ramus fractures often are mistaken for malignant lesions.
Sacral, iliac, and supra-acetabular fractures often are difficult to detect.
Computed Tomography
Axial CT of the sacrum reveals fractures (arrows) in both sacral alae. Note the sclerosis of the adjacent bone.
Coronal CT of the sacrum demonstrates fractures (arrows) in both sacral alae. These fractures are oriented parallel to the sacroiliac joints. Note the prominent adjacent sclerosis.
Axial CT of the pubis reveals insufficiency fractures (arrows) in both parasymphyseal regions. Total hip replacement is an additional predisposing causative factor.
Axial CT of the sacrum reveals 2 large Tarlov cysts (arrowheads) in the sacrum. The sacral insufficiency fractures produce anterior cortical breaks (arrows).
Findings
- On CT, sacral fractures typically are oriented vertically and are located parallel to the sacroiliac joints (see Image 2).
- A linear fracture line with surrounding sclerosis is observed (see Image 3).
- Pubic fractures are seen as a lytic fracture line often surrounded by callus (see Image 4).
- Typically, a soft tissue mass is absent, bone destruction is lacking, and adjacent fascial planes are preserved.
- CT also is useful for detecting large bony sacral defects such as Tarlov cysts (see Image 5) and for the diagnosis of coexisting malignant lesions.
Degree of Confidence
CT findings may be definitive for the diagnosis of insufficiency fractures of the pelvis. CT is specific and is useful as an alternative to MRI or bone scintigraphy when radiographs are inconclusive.
Magnetic Resonance Imaging
Axial T1-weighted MRI of the sacrum demonstrates decreased signal in the body and both alae of the sacrum. Bilateral sacral insufficiency fractures were confirmed by CT.
Axial T2-weighted MRI of the sacrum (same patient as in Image above) demonstrates linear bands of decreased signal in both sacral alae, parallel to the sacroiliac joints. Traces of fluid are observed within the fractures (small arrows). Adjacent edema is seen as areas of increased signal. Bilateral sacral insufficiency fractures were subsequently confirmed by CT.
Axial CT of the sacrum (same patient as in Image above) reveals insufficiency fractures in both sacral alae and the sacral body (arrows).
Findings
- MRI shows decreased signal on T1-weighted images and increased signal on T2-weighted images.
- In the sacrum, signal changes are seen as linear bands within the sacral ala and body; such bands are parallel to the sacroiliac joints (see Image 6).
- On T2-weighted images, the fracture line may be seen if it is surrounded by adjacent marrow edema (see Images 7-8).
Degree of Confidence
MRI is highly sensitive and highly specific. MRI cannot be used in patients with pacemakers — a significant limitation in the elderly population.
Nuclear Imaging
Bone scan of the pelvis reveals a butterfly-shaped area of uptake in the sacrum (arrows). Focal uptake in the pubis (arrowhead) corresponds to an associated parasymphyseal insufficiency fracture.
Bone scan of the pelvis reveals an incomplete (or partial) H-shaped area of uptake in the sacrum (arrows). Bilateral parasymphyseal insufficiency fractures (arrowheads) are present.
Bone scan of the pelvis demonstrates a horizontal linear dot pattern of uptake in the sacrum.
Bone scan of the pelvis demonstrates a linear area of uptake in the pubis (arrowheads). A concomitant H-shaped insufficiency fracture of the sacrum is observed.
Findings
- In nuclear studies, the typical H-shaped or butterfly pattern of uptake in the sacrum is diagnostic of insufficiency fracture. The vertical limbs of the H lie within the sacral ala, parallel to the sacroiliac joints; the transverse limb of the H extends across the sacral body (see Image 9).
- Other sacral variant uptake patterns occur frequently and include the unilateral ala, incomplete H (see Image 10), and horizontal linear dot (see Image 11) patterns.
- Iliac fractures are seen as linear areas of uptake.
- Pubic and supra-acetabular fractures produce areas of linear or focal uptake.
- Concomitant findings of 2 or more areas of uptake in the sacrum and at another pelvic site are considered diagnostic of insufficiency fractures of the pelvis (see Image 12).
Degree of Confidence
The degree of confidence may be high. Nuclear studies are highly sensitive and highly specific when a typical pattern of sacral uptake or concomitant sacral and pubic uptake is observed. If a typical pattern of abnormality is not present, the bone scan is much less specific.
False Positives/Negatives
For variant or incomplete patterns of uptake, the findings may be mistaken as signifying malignancy or other diseases. CT or MRI is useful in such cases.
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 Imaging: Pelvis, Insufficiency Fractures |
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References
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Further Reading
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Fracture, Pelvic
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Keywords
pelvis insufficiency fracture, pelvis fracture, pelvic fracture, fracture of pelvis, stress fracture, pubic bone, parasymphysis, pubic rami, unstable pelvic fracture
